Waterproof, breathable footwear is made with air-permeable and water-permeable outer upper material such as leather and textile materials. Waterproofness with simultaneous water vapor permeability is achieved with the use of a liner laminate that has a waterproof water vapor-permeable functional layer which is provided with a backing fabric on the one side facing towards the outer upper material. On the other side of the functional layer, a lining material is also provided so that it is on the side away from the upper. The bottom end of the upper is sewn to an insole by means of a closing seam. A plastic or synthetic outsole is injected or injected molded onto the insole and the bottom end of the upper connected to it so that both the joining seam between the insole and end of the upper, as well as the end of the upper itself are enclosed by the plastic or synthetic of the outsole and thereby sealed.
The bottom ends of the outside upper and inside upper have thus far been sewn together and to the insole by means of a single seam. The underlying idea here is to position the seam in the region made waterproof by the outsole thus protecting it from water penetrating from without.
However, when water reaches the upper outer material in such shoes, moisture is found in the lining a short time later. The reason for this proved to be that the upper outer material used for such shoes, be it leather or a textile material, conducts water not only in its transverse direction, but also in its longitudinal direction. In this fashion, water that enters the upper material from the outside can travel through the upper material within the backing fabric or on the functional layer of the liner laminate to the bottom end of the upper lying within the outsole to reach the lining of the inside upper by means of two mechanisms. Water that has traveled in the upper material and in the backing fabric or on the functional layer to the seam joining the outside upper, the inside upper and the insole, reaches the liner material of the inside upper through the seam openings in the functional layer and the wick-like water-conducting seam threads. Also, in the manufacture of the inside upper it often happens that the textile threads of the textile reverse side and/or the liner material on the cutting edge of the bottom end of the inside upper extend around the cutting edge of the functional layer and act as water bridges from the upper material to the liner material.
Since the liner material ordinarily consists of a material with strong moisture absorption capacity, water that has reached the lining through this water bridging mechanism spreads very quickly in the lining. It takes at most only about 10 minutes for the liner material to become moist once water has come in contact with the outer upper material.
Although the water conductivity of the backing fabric has indeed been reduced by using monofilament textile materials, it cannot be completely eliminated.
A remedy for the aforementioned water bridging mechanism is described in U.S. Pat. No. 4,899,465. In this case, the outer material of the upper does not extend to the bottom end of the inside upper, but rather the bottom end of the outside upper is formed from a joining strip running within the outsole, the top end of which is sewn to the top of the outside upper and the bottom end of which is sewn by means of a closing seam to both the bottom end of the inside upper and to the insole. The joining strip consists of a material that is not water-conductive, and may be a spacer of net or mesh formed from a monofilament material. Water that reaches the top seam with the net within the outside upper cannot penetrate further to the bottom joining seam between the net, inside upper and insole. In addition, during injection molding of the outsole, the net is penetrated by liquid plastic which reaches the region of the backing fabric or the functional layer lying behind the net. In this fashion the backing fabric is glued together, its water conductivity is suppressed and the region of the functional layer within the injection molded outsole is sealed.
These measures proved to be very effective in suppressing water bridges between the outside upper and the lining. It is necessary to use a net with a width of at least 10 mm, thus ensuring a minimum inflow opening of about 5 mm for the liquid plastic of the outsole during the injection molding process. The remaining 5 mm is required for seam overhang to sew one end of the net to the outside upper and the other end to the inside upper and the insole. Since the seam between the net and the outside upper in the finished shoe must be covered by the injection molded outsole, this technique requires a minimum immersion depth of the upper in the injection molded outsole of 14mm. This leads to a corresponding minimum height of the outsole edge. For fashion reasons, shoes are also now desired with much thinner injection molded outsoles.
The net used for shoes of the aforementioned type ordinarily consists of a relatively rigid material. It is therefore difficult to fashion the net without causing an increased number of folds, especially in the region of the shoe tip and thus without a deterioration in fit of the shoe in the region of the insole. There is a need to improve the fit of the shoe and permit injection molding of a thinner outsole.